Carbon dioxide removal via Amine treating

[Aliceglen]

Hi everyone,
I am currently working on a project to remove carbon dioxide from natural gas. The main components in the gas are:
Methane 91.86
Nitrogen 0.031
Carbon dioxide - 1.973
These are mole percent values. The rest of the gas is comprised of other hydrocarbons. There are no sulphur or sulphide components.
The project seeks to produce 175 MMSCFD of natural gas at a carbon dioxide level of 0.5 mol %.

I was wondering if there was any information on Activated MDEA and DGA, such as:
Absorption rate
Loading capacity
Sensitivity to impurities.

Any information that can help me decide on which amine to use would be greatly appreciated

 

[Zoobie]

I have found that the amine vendors are very helpful in this regard. They can properly simulate their own solvents which can then be used as input into your design. Dow (Ucarsol solvents)has helped me before by doing case studies for proposed projects....of course we did buy their product.

 

[Montemayor]

Alice:

Zoobie is absolutely correct. The Amine manufacturers (not vendors) will be very cooperative and will assist in evaluating the various amines that can be employed in this specific application.

Normally, from the analysis given, I would employ MEA. However, I don't know what "impurities" are present or can suddenly appear. I also don't know the available utilities - like steam for reboiler service. Steam usage may be important, as well as CO₂ loadings.

 

[Chemeng1122]

As mentioned above, contacting the amine manufacturers (or vendors, depending on where you are) would be best. Which amine you choose would be largely dependant on your treating pressure, which you did not specify.

For a bulk CO2 removal application, I dont think that DGA would be the best option (unless you are at very low pressure), as the regeneration duty would likely be higher than other options. aMDEA or one of the other formulated amines from the manufacturers would probably be better suited to the application. From Huntsman, probably from the Jefftreat M500 series or the MP series, Dow would most likely recommend something from the Ucarsol AP800 series or the CR300 series. I am less familiar with Ineos products.

Depending on where you are in the world, BASF may charge liscencing fees for use of their aMDEA process (I think anywhere in the world except North America).

For CO2 loadings, it depends a lot on system pressure (more correctly - CO2 partial pressure in the system). Most of the amines listed above follow the rule of thumb of a max rich loading of 0.5 m/m, though BASF does not really publish rich loadings for aMDEA. They simulate based on an approach to equilibrium %, which they have told me relates to a rich loading significantly above 0.5 m/m. Again, contacting the companies directly would be the best idea.

As far as the impurities, you would have to be more specific. Are you talking about hydrocarbons, production chemicals, corrosion inhibitors, ...? Impurites are not a good thing in any amine system.

Andrew Lechelt
Technical Support Engineer
Quadra Chemicals

http://www.quadrachemicals.com

 

[Aliceglen]

Thanks a lot for the information given. The only information that I am not sure that I will obtain from the manufacturer is whether to include an inlet separator before the amine separator (to remove hydrocarbons and other contaminants) even though there is a slug catcher present.

Is there a real need for this separator or will I have to contact the manufactures regarding the sensitivity of DGA and aMDEA to hydrocarbons and impurities

 

[Chemeng1122]

Most manufacturers would recommend that you install a coalecser or other high efficiency separator in addition to the slug catcher. The slug catcher will stop the large amount of liquids that come in from the field, usually with pigging, but wont necessarily stop fine liquid droplets that are entrained in the gas stream.
We have seen in may cases where there is a slug catcher but no coalescer, significant foaming issues arise because of the continuous contamination from the small lioquid droplets.

It would also depend alot on your gas composition. If you have very dry, lean gas then you may not need a coalescer, but the fact that you have a slug catcher suggests otherwise. I would suggest that you look at a coalescer in addition to the slug catcher. Contacting a manufacturer of coalescers would give you an idea on sizing and cost (higher liquid load, larger vesser and lorger cost).

Andrew Lechelt
Technical Support Engineer
Quadra Chemicals

http://www.quadrachemicals.com